Conventionally, an image capturing apparatus for transmitting a captured image to a receiving apparatus includes commands for allowing an external apparatus to change the settings of the image capturing apparatus and designate the start of image distribution. Known examples of these commands are those defined by standards formulated by the ONVIF (Open Network Video Interface Forum).
In the ONVIF specifications (http://www.onvif.org/specs/DocMap.html), commands formulated by the ONVIF are described.
The above-described commands include, for example, a command for changing, from an external apparatus, the resolution of image data to be generated by an image capturing unit of the image capturing apparatus. The above-described commands also include a command for changing the resolution of a distribution image to be distributed to an external apparatus when the distribution image is generated by encoding image data generated by the image capturing unit. For example, in the ONVIF standards, a SetVideoSourceMode command is defined as the former command, and a SetVideoEncoderConfiguration command is defined as the latter command.
Furthermore, in addition to the ONVIF standards, Japanese Patent Laid-Open No. 2005-323007 has disclosed an image capturing apparatus including a control unit for controlling the expansion and compression of a captured image.
Unfortunately, there is a problem that if only one of the resolution of image data to be generated by the image capturing unit and the resolution of a distribution image to be generated by a compression encoding unit is changed, mismatching occurs in a combination of the two resolutions and this makes the generation of the distribution image impossible in some cases. Also, in a case like this, it is necessary to transmit a command for correctly changing the other resolution from an external apparatus to the image capturing apparatus, in order to cancel the mismatching and correctly generate the distribution image. This complicates the user's operation.
Assume that the output resolution of the image capturing unit is 1,600×1,200 pixels (UXGA), and the output resolution of the compression encoding unit is 1,280×1,024 pixels (SXGA). In this case, if the output resolution of the image capturing unit is changed to 1,024×768 (XGA), the compression encoding unit in which a higher output resolution is set may become unable to generate any distribution image. Assume also that the output resolution of the image capturing unit is 1,600×1,200 pixels (resolution aspect ratio=4:3), and the output resolution of the compression encoding unit is 1,280×1,024 pixels (resolution aspect ratio=4:3). In this case, if the output resolution of the image capturing unit is changed to 1,920×1,080 (full HD, resolution aspect ratio=16:9), the compression encoding unit in which a different resolution aspect ratio is set may become unable to generate any distribution image.
If this is the case, before obtaining a video stream from the image capturing unit, the user must change the output resolution of the compression encoding unit to a resolution, such as 1,024×768 (XGA) or 1,920×1,080 (resolution aspect ratio=16:9), which matches the output resolution of the image capturing unit, and this complicates the operation.